110 

3 

>py 1 




BULLETIN OF THE 



No. 151 




Contribution from the Bureau of Plant Industry, Wm. A. Taylor, Chief. 
September 19, 1914. 

EXPERIMENTS IN CROP PRODUCTION ON FALLOW 
LAND AT SAN ANTONIO. 

By C. R.'Letteer, Assistant, Office of Western Irrigation Agriculture. 
INTRODUCTION. 

The practice of fallowing land, varies widely in different regions. 
In the experiments conducted at San Antonio, Tex., and reported 
in this paper the word "fallow" is used to mean thorough cultiva- 
tion of the land from the time it is plowed after the removal of a 
crop throughout the next season and until the crop is planted at 
the beginning of the second season. The fallow period at San 
Antonio varies from 16 to 19 months, depending on the crops grown. 
The chief ostensible purpose of fallowing in this region is to store 
in the soil for the benefit of the next crop the moisture which falls 
during the fallow period. 

In order to determine whether or not this practice is to be recom- 
mended m the San Antonio region, the experiments reported herein 
were started ia 1910. 

CLIMATIC CONDITIONS. 

The climatic conditions at San Antonio are much different from 
those in the dr^^-f arming regions farther north. 

The conditions fluctuate irregularly from semiarid to humid. 
Droughts of many weeks' duration are common and may come at 
almost any season of the year, but they are more frequent and more 
serious during the summer months. The mean annual rainfall at 
San Antonio for a period of 33 years, as reported by the United 
States Weather Bureau, is 26.83 inches. The mean annual rainfall 
for the 7-3"ear period from 1907 to 1913, inclusive, as measured at 
the San Antonio Experiment Farm, 5 miles south of the city, is 
24.66 inches. WhUe the normal precipitation would appear to be 
sufficiently large to make crop production fairly certain, yet on 
account of the unequal distribution of the rainfall and the high 

• rroni January, 1910, to October, 1911, the experiments here reported v ere imder (he direct supervision 
of Mr. S. H. Hastings, superintendent of the San Antonio Experiment Farm. Mr. C. R. Letteer has had 
direct eha-fe of the work since October, 1911. 



2 



BULLETIN 151, U. S. DEPAETMENT OF AGRICULTUEE. 



evaporation the effect of the precipitation is much lessened. The 
mean annual evaporation from a free water surface, as measured at 
the experiment farm for the 7-year period specified, is 65.88 inches. 

The winters are mild, 3-et periods of cold weather or "northers" 
are not infrequent during the winter season. The thermometer 
seldom registers a temperatm-e below 15° F. in winter, and conse- 
quently plant growth continues practically throughout the year. 

SOIL CONDITIONS. 

Hie San Antonio Experiment Farm is located on what is called 
locally black "hog-wallow land. " This local name is due to the fact 
that the soil, when drying, shrinks and opens long, wide cracks, and 
the filluig of these cracks \\"ith loose surface sod results in irregular 
depressions, which reseml^le hog wallows. The soil Is a black clay 
loam, having a rather small proportion of sand and becoming very 
sticky when wet. It is classified by the United States Bureau of 
Soils ' as Houston black clay loam and San Antonio clay loam. 

The first 3 feet of sod is fairly uniform in character and is under- 
lain with, a white gravelly material which is rich in lime. This under- 
Ijdng gravel has a l elatively low moisture-holding capacity, while the 
surface soil has a high moisture-holding capacity, averaging from 
25 to 30 per cent. Wlien wet, the soil has a tendency to pack 
and become imper%'ious, so that during torrential rains the loss of 
water from run-off is high. The soil is rich in mineral plant food and 
produces abundant crops when su])pHed with sufficient moisture. 

FALLOWING EXPERIMENTS. 

In 1910 experiments were inai gurated for the purpose of studying 
the effect of producing a croj) oidy on alternate years, as compared 
with producmg a crop every year on the same land. The crops of 
1910 were grown on land wliich had not been previously fallowed, 
so that the results for that year are not considered here. The results 
here presented are from the ycais 1911. 1912, and 1913. 

The crops used in those experiments were corn, cotton, and winter 
oats. For this puipose six |-acre plats were used, as follows: Plats 
A4-1 and A4-2 were used alternately for cotton, one plat bemg 
cropped and the other fallowed each year. In a similar way plats 
A4-3 and A4-4 were used for corn and A4-5 and A4-6 for ^vinter oats. 
For purposes of comparison -with these biennially cropped plats, use 
has been made of results obtained from three plats which are part of 
another experiment. These thi-ee plats are cropped each year and 
are given the same tdlage treatment as the alternately cropped plats, 
except that the fallow period is 12 months shorter. The plats that are 
cropped annually have been under test since 1909, when the large 

• Field Operations of the Bureau of Soils, 1904. 

OCT 8 JS14 



B 1'^^ 

L.3 CROP PRODUCTION ON PALLOW LAND AT SAN ANTONIO. 3 

rotation and tillage experiment of which they are a part was started. 
The plats which are continuously cropped are as follows: B5-1, 
■ corn; B5-3, cotton; and B5-8, oats. The plats are each 264 feet long 
and 41.25 feet wide, and they are separated by alleys 4f feet wide. 

TREATMENT OF THE PLATS. 

Figure 1 shows graphically the cropping system practiced on the 
plats considered in this report, from the time the biennial cropping 
experiments were started until the close of the year 1913. 

The winter oats were seeded early in November and harvested in 
May, the corn was planted the latter part of February and harvested 



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Fig. 1.— Diagram showing the cropping system practiced on the plats where biennial cropping has been 
tested in comparison with continuous cropping at the San Antonio Experiment Farm. 



in July, and the cotton was planted early in April and the harvest 
completed in October. 

In all cases except plat B5-8 (oats cropped annually) the plats 
were plowed about 8 inches deep as soon as practicable after the crop 
was removed . Plat B5-8 was left unplowed until just before planting 
time. After plowing, the plats were harrowed after the first heavy 
rain came, to soften the clods. They were then harrowed or disked 
after each rain of consequence and also whenever it was necessary 
to keep them clear of weed growth and to maintain a soil mulch. 
For the most part the spike-tooth harrow was sufficient to maintain 
an adequate mulch throughout the greater part of the fallow period . 



4 



BULLETIN 151, U. S. DEPAETMEXT OF AGBICULTUBE, 



YIELDS OBTAINED. 

Table I gives the yields of various crops from the plats cropped 
bionnially, as compared with the yields of the same crops on plats 
cropped armually, and the average yields of the various crops from 
all plats planted to each crop in the rotation experiments. The aver- 
age pelds arc obtained by con-sidering all of the plats in the rotation 
experiments and should be fairly representative of results from good 
farming in that region. 

Table I. — Crop yiel/ls from plats cropped biennially, as compared with plats cropped 
annually and with all plcts xtsed for these crops in the rotation experiments.^ 



Biennial cropping. 



of all rotv 
tion plats. 



qropping. 



XambtT of 

plat'! 
averaged. 



Corn bushels.. 3.2 

Cotton pounds.. 318.0 

Oats bushels.. 10.1 



Com bushels. 

Cotton pounds. 

Oats bu-'hels. 



Corn bushels. . 30. 7 

Cotton pounds.. 350.0 

Oats bushels.. 3S.0 



Com bushels.. 19. .5 

Cotton pounds..' 372.0 

Oats Inishels.. 2S. 4 



S9.2 
7L3 
160.5 



92.9 
94.6 
18L5 



26.6 
474.0 

2a 4 



2L7 
476.0 
12.3 



bicn: 
ing, 
woui 



■ ■ rondiioled on S2 quarter-acre plats. Ther mclude continuous cropping, 
■■ ear, and 4-year rotations, combined with various tillaee methods, manur- 
neral, it would be expected that the average yields in these experiments 
i a ined from the continuously cropped plats. 

It is u in Table I that in no instance has cotton or com yielded 
as much on biennially cropped as on annually cropped land. The 
average pelds of cotton and corn on all the rotation plats have been 
higher than those secured friDii cither i)icniiial cropping or annual 
croppmg, indicating that neither fallowing nor continuous cropping 
for corn and cotton is to be recommended as a general practice imder 
San Antonio conditions. 

On the other hand, -s^inter oats on land biennially cropped have 
consistently yielded liigher than where planted annually on the 
same land and higher than the average from all oat plats in the 
rotation experiments. 

VEGETATIVE GROT\TH OF CROPS ON FALLO^TD L.\ND. 

It has been observed during the past two years that during the 
gi'eater part of the growing period oats made a less rank growth on 
the fallowed plat than on the plats in the rotation experiments. 



CKOP PKODUCTIO^" ON FALLOW LAND AT SAN ANTONIO. 5 

This comparatively light vegetative growth appears to have been 
favorable to the production of grain. In 1912 and 1913, especially 
the latter season, oats on the rotation plats lodged badly, o\'\Tiig to 
excessive vegetative growth. It has been found at San Antonio that 
any treatment which has a tendency to retard the early vegetative 
growth of the oat plant results in increased yields of graia. An 
instance substantiating this statement is afforded by the unfavorable 
results from manuring on land planted to oats to be harvested for 
grain. In a 4-year test with oats, manuring has noticeably decreased 
the yield of grain in two out of the four years, while in the other two 
years the yields were practically the same as those obtained from 
nnm annred land. It appears, therefore, that the increase in yield of 
osJbs on fallowed land has not been due to the fact that conditions 
were more favorable to growth, but rather to a depressing effect on 
the vegetative growth. 

Crops grown on fallowed land have invariably shown irregular and 
slow early development as compared with the same crops on other 
plats. The corn and cotton on the fallowed plats have been notice- 
ably smaller than on the other plats in the rotation experiments, and 
the plants have lacked imiformity in size and appearance. Observa- 
tions on other plats of the experiment farm where cotton has been 
grown on fallowed land corroborate this conclusion. While the 
differences -with oats have not been so marked, in 1913 the oats on 
fallowed land were smaller and made slower growth than on land 
continuously cropped or having other treatments. On account of 
the difficulty -R-ith the lodging of grain crops, as abeady indicated, the 
depressing effect of faUomng on the growth of the plants results in 
high yields of oats, while it has the opposite effect on corn and 
cotton. 

SOIL-MOISTURE STUDIES. 

Soil-moisture determinations have been made on the fallowed plats 
considered in this report and also on the continuously cropped plats 
devoted to the same crops. Samples have been taken monthly or 
oftener during the summer throughout the three years. A standard 
soU tube was used for securing the samples. At each samphng two 
cores were taken from different parts of the plat, corresponding foot- 
sections being composited to a single 'sample. Thus either three or 
six samples were secured from each plat, depending upon the depth 
to which the sampling was done. In most cases samples were taken 
to a depth of 6 feet. 

In figures 2, 3, and 4 the diagram at the top shows the crop, 
stubble, and fallow periods for each plat considered in this report, 
and the cxu-ves below show the moisture content of the different 
plats at the time the moisture determinations were made during the 
four years from 1910 to 1913, inclusive. 



6 



BULLETIN 151, U. S. DEPARTMENT OF AGEICULTUEE. 



Moisture determinations have been made on each oi the plats at 
planting time and just before or just after haiTest, to determine the 



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i i CO/9A/ I 




Fk; J !' of the soil on plat B.>-1, which was cropped 

,111; ^vcre cropped biennially to com, at the San 

Aiii ; ,, I 1,1.1., I r. 1013. On each sampling date all the plats 

were .-ampl<'<l to a uniform dc'ijih, in must cases u led, but in some instances 3 feet. 

amount of moisture present at planting time and the amount of 
stored moisture used from eacli plat. 



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T : 














































































1 


1 
! 









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Fig. 3. — Diagram showing the average moisture content of the soil on plat B.5-3, which was cropped 
annually to cotton, and on plats A4-1 and A-1-2, which were cropped biennially to cotton, at the 
San Antonio Experiment Farm, January, 1910, to October, 1913. On each sampling date all the 
plats were sampled to a uniform depth, in most cases 6 feet, but in some instances 3 feet. 

By observing carefully the curves showing the moisture content 
in the various plats it -ftdll be seen that the moisture content of the 



CROP PKODUCTION ON FALLOW LAND AT SAN ANTONIO. 7 



plats of corn (fig. 2) and cotton (fig. 3) was generally highest in the 
spring at about planting time for these crops; that there was a gen- 
eral decline in the moistiu-e content of the cropped plats until har- 
vest and also a sHght decHne in the moisture content of fallowed 
plats; and that there was only a slight difference in the moisture 
content of the fallowed and continuously cropped plats at either 
planting or harvest time, the tendency being for the curves to coin- 
cide at these periods. 

The moisture content of the oat plats (fig. 4) was generally highest 
during the months of January and February and lowest in June, at 
about harvest time. At planting time for oats in the autumns of 

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Fig. 4.— Diagram showing the average moisture content of the soil on plat B5-8, which was cropped 
annually to oats, and on plats A4-5 and A4-6, which v/ere cropped biennially to oats, at the San 
Antonio Experiment Farm, January, 1910, to October, 1913. On each sampling date all the plats 
were sampled to a imiform depth, in most cases 6 feet, but in some instances 3 feet. 



1910 and 1912 the moisture content of the fallowed plat was somewhat 
higher than that of the continuously cropped plat, and in 1911 it was 
nearly the same. At harvest time in 1911 and also in 1912 the 
moisture content of the fallowed plat was somewhat lower than that 
of the continuously cropped plat, and in 1913 the moisture content 
of both plats was about the same. 

It appears from this that fallowing resulted in a higher moisture 
content in the fall at planting time for oats, and that when the land 
remained fallow until time for planting corn and cotton, fallowing 
did not store any appreciable quantity of moisture in the soil in 
excess of that stored in land continuously cropped, plowed in the 
fall, and left fallow during the winter. 



8 



BULLETIN 151, U. S. DEPARTMENT OF AGBICULTUBE. 



For the most part the curves show only slight variations in the 
amount of moisture present in the fallowed and continuously cropped 
plats during the period when crops were on the land. There was a 
somewhat higher moisture content in the soil of the fallow plats at 
the time when crops were growing on the other plats; but, as already 
stated, the difference generally disappeared by the next planting 
time. 

EUN-OFF FROM FALLOWED PLATS. 

The uniformity in soil-moisture content at planting time, already 
noted, is probably accounted for by the higher loss hy run-off from 
fallow plats than from those which were cropped every year. Dur- 
ing the years covered by this report the precipitation during the 
winter and early spring was comparatively heavy. Consequently, 
so far as the rainfall dunng the ^\^nter and spring immediately ]ire- 
ceding corn and cotton planting was concerned, land cropped each 
year and plowed as soon as possible after the removal of the crop 
had the same opportunity to store moisture as fallowed land had 
during the same period. Even though the fallowed land contained 
a larger amount of moisture at the time of seeding oats in the fall, 
a larger amount of run-off from the fallowed plats during the winter 
would result in approximately uniform moisture conditions in all 
the plats at the time of planting corn and cotton the follo\ving 
spring. That there is a diflference in the run-oflf from the diflFerent 
plats is proved by the results of determinations shown in Table II. 

On February 16, 1912, three days after a rain of 3.3 inches, soil 
samples wore taken on one plat of oats and on five fallow plats where 
the length of time since plo\nng varied from 3 to 18 months. Table 
II shows the moisture content at the last sampling before the rain and 
again three days after the rain, together with the increase in moisture, 
the run-off in inches, and the percentage of rainfall lost by run-off. 

On February 26, samples were again taken on the same plats after 
a 2-days' rain of 2.9 inches. The results are also given in Table II. 

Table II. — Absorption and run-off from rains in February, 1912, San Antonio Experi- 
ment Farm. 







Samples taken on Feb. 16, three days after a 3.3-mch rain. 


Plat No. 


Fallow period 
or crop. 


Average moisture 
content in 3 feet. 


Increase. 


Run-off. 






5 days 
before 
rain. 


3 days 
after 
rain. 


Per cent. 


Inches. 


Inches. 


Percent- 
age of 
rainfall 


A4-1 


3 months 


Percent. 
15.8 
19.1 


Per cent. 
19.9 


4.1 


1.92 


1.3S 


41.8 


A4-2 


15 months. 


21.6 


2.5 


1.17 


2. 13 


64.5 






17.2 


19.8 


2.6 


1.22 


2.08 


63.0 


A4-4 


18 monttis 


20.0 


23.0 


3.0 


1.40 


1.90 


57.5 


A4-5 


6 months 


18.4 


20.6 


2.2 


1.03 


2.27 


68.8 


A4-6 


Oats 


IS. 1 


22.3 


4.2 


1.96 


1.34 


40.6 















CEOP PRODUCTION ON FALLOW LAND AT SAN ANTONIO. 



Table II. — Absorption and run-off from rains in February, 1912, San Antonio Experi- 
ment Farm — Continued. 



Plat No. 


Fallow period 
or crop. 


Samples taken on Feb. 26, one day after a 2.9-inch rain, when 
the sou was aheady wet. 


Average moisture, 
content in 6 feet. 


Increase. 


RuB-oiT. 


7 days 
before 
rain. 


1 day 
after 
rain. 


Per cent. 


Inches. 


Inches. 


Percent- 

a^o of 
rainfall. 


A4-1 

A4-3 

A4-4 

A4-5 

A4~6 


3 months 

IS months 

6 months 

Oats 


Per cent. 
15.2 
16.8 
15.3 
16.7 
15.5 
16.3 


Per cent. 
16.6 
17.2 
16.8 
17.8 
16.2 
18.4 


1.4 
.4 

1. 1 
.7 
2.1 


1.3 
.37 

1.4 

!66 
1.96 


1.61 
2. 54 
1.51 

2^25 
.95 


55.3 
87.1 
51.7 
64.6 
77.3 
32.6 



Table II shows that the run-off from land that had been fallow for 
several months was greater than from land plowed a comparatively 
short time before the heavy rains. The proportion of run-off fro-m 
the second rain was somewhat greater than that folio-wing the first 
rain, and the difference in run-off from plats fallowed for a short time 
and from those wliich had been fallow for a longer time was more 
marked. The run-off from the oat plat was materially less following 
both rains than that from any of the fallow plats. 

ECONOMIC CONSIDERATIONS. 

T.he question of whether it is desirable to make a practice of 
biennial cropping for certain crops must be considered from two 
standpoints: (1) The effect upon the crop and (2) the 'cost of pro- 
duction as compared with aimual cropping. It must be remembered 
that in the fu'st case only one crop is grown in two years and that 
fixed costs, such as the interest on the investment in land for two 
years, must be charged against one crop. Under the conditions at 
San Antonio, where plant growth continues practically the entire 
year, making necessary the cultivation of the fallow to kill weeds 
and maintain a mulch, the expense of fallowing is nearly, if not quite, 
as much as that of growing a crop on the land. Other items, such as 
the depletion of the humus and the possible ultimate effect on fertility, 
are matters deservuig consideration in connection with the practice 
of biennial cropping. It must be concluded, then, that even though 
biennial cropping gave increased yields of winter oats at San Antonio 
it is not necessarily desirable as a farm practice in growing that crop 
there. In other words, the results of these experiments indicate 
that biennial cropping is not to be recommended for the San Antonio 
region, at least for cotton, corn, and oats. 



10 BULLETIN 151, U. S. DEPARTMENT OF AGEICULTUBE. 



SUMMARY. 

(1 ) Tests of biennial cropping in comparison vaih. annual cropping 
have been carried on at the San i\jitonio Experiment Farm for 
three years. 

(2) The yields of com and cotton have been less on biennially 
cropped land than on annually cropped land. The yields of winter 
oats have been someAvhat larger on the biennially cropped land. 

(3) Soil-moisture studies made in connection with these tests do 
not sliowiuiy important difTerencos in the amount of soil moisture 
prescnl in fallowed land and in continuously cropped land at planting 
and liaivcsi lime for corn and cotton. In the plats used for oats 
there %vas nioie moisture present at planting and less at harvest time 
on tlio bicnniuUv cropped land than on the annually cropped land. 
In other words, the oats grown biemiially used more water and made 
less vogolativo growth, but gave larger yields. 

(4) Obsci\-aii()ns mudo after heavy rains show that in most cases 
the proportion of run-off from heavy rains was greater on land which 
had boon fallow lor several months than on land which had been 
fallow for a eoniparutively short time. The run-off from an oat plat 
was less than from any of the fallow plats. 

(5) Considering both crop jnelds and cost ot production, the results 
of these experiments indicate that biennial cropping, at least for 
corn, cotton, and oats, is not to be recommended for the San Antonio 
region. 



WASHINGTON : GOVEBXMINT PRINTING OFFICE : 1914 



LIBRARY OF CONGRESS A) 

llllllllllllllllllll" 

021 531 644 



